What to prune & when, from BH: Early-spring bloomers, such as lilac, forsythia, and rhododendron, bear flowers on wood formed the previous year. The best time to prune them is late spring -- immediately after they finish blooming. If you prune them later in the growing season or during winter, you'll remove flower buds and decrease the amount of spring blooms. Login Login 0 repins 0 comments 0 likes